Seat reclining devices have locking mechanisms that allow for adjustment of the inclination angle of the seat back relative to the seat cushion. The seat back can be tilted forward to a predetermined position by means of the seat reclining device. By operating a first operation lever, the seat back can be switched between a locked state, in which the seat back is restricted from tilting relative to the seat cushion, and an unlocked state, in which the seat back is allowed to tilt. The seat back is urged to lean forward by forward tilt urging means. When unlocked, therefore, the seat back is tilted forward by the forward tilt urging means. The forward leaning seat back is then pulled back and returned to an upright position suitable for seating. Since, generally, the seat back is locked when it comes to the front limit of reclining, the passenger has to adjust the inclination angle of the seat back every time he or she sits on the seat. Manipulation of the seat back after it is tilted forward may therefore be not easy.
There has been proposed a seat reclining device that is capable of remembering an angular position of the seat back where it is located immediately before being tilted forward and setting the seat back to the angular position that has been remembered, when the forward tilted seat back is pulled back. With this, the seat back only needs to be pulled back up to be set again at the angular position where it is located before being tilted forward. Manipulation of the seat back is therefore easier when pulling back the seat back and seating. In many cases, however, the memory mechanism that remembers the angular position of the seat back is located at a different position from the locking mechanism, which causes an increase in the number of parts and cost.
Patent Document 1 discloses a seat reclining device equipped with a locking mechanism and a memory mechanism. The locking mechanism 100 is made up of a first member 101, a second member (not shown), a plurality of locking members 103, a cam 104, and a spring (not shown), as shown in FIG. 26(A). The first member 101 is attached to one of the seat cushion and the seat back, and has internal gear 106 around an operation shaft 105. The second member is attached to the other one of the seat cushion and the seat back, and rotates around the operation shaft 105 relative to the first member 101. The locking members 103 are attached to the second member and each have external teeth 107. The cam 104 is connected to the operation shaft 105 and urged counterclockwise in FIG. 26(A) by a spring. When the cam 104 rotates counterclockwise by the urging force, the locking members 103 are each pressed radially outward by the cam 104. The external teeth 107 thereby mesh with the internal gear 106, so that the seat back is locked. Operating a first operation lever rotates the cam 104 clockwise with the operation shaft 105. The locking members 103 are each moved radially inward by the cam 104. The external teeth 107 thereby disengage from the internal gear 106, so that the seat back is unlocked. There are two unlocked states of the seat: in one state, the seat back is allowed to tilt without an angular position being remembered by the memory mechanism 110, and in the other state, the seat back is allowed to tilt with an angular position being remembered by the memory mechanism 110.
The memory mechanism 110 includes a housing recess 111, engagement portions 112, and a memory plate 113. One engagement portion 112 each is provided on each locking member 103. The housing recess 111 is provided to the first member 101 and formed in a cylindrical shape. The engagement portions 112 each protrude from the locking members 103 along the operation shaft 105. The memory plate 113 is formed in an annular shape that is cut at one point. The memory plate 113 is housed in the housing recess 111 while being reduced in diameter. An engagement receiving portion 114, formed as a recess, is provided in the inner circumferential surface 113B of the memory plate 113. The engagement portions 112 engage with and disengage from the engagement receiving portion 114.
To tilt the locked seat back to a desired angle, the first operation lever is operated to rotate the operation shaft 105. In this case, the first operation lever is moved by an angle necessary for unlocking the seat back so that it can tilt, without its angular position being remembered by the memory mechanism 110. At this time, the cam 104 is rotated clockwise in FIG. 26(A) by a certain angle with the operation shaft 105. The rotation of the cam 104 slightly moves the locking members 103 radially inward, as shown in FIG. 26(B). As each locking member 103 moves, the external teeth 107 disengage from the internal gear 106. The seat back is thus unlocked. The engagement portion 112 is half engaged with the engagement receiving portion 114. When the seat back is tilted forward in this state, the locking members 103 each rotate with the memory plate 113 relative to the housing recess 111. At this time, the outer circumferential surface 113A of the memory plate 113 slides on the inner circumferential surface 111A of the housing recess 111. When the first operation lever is returned to its initial position, the cam 104 presses each of the locking members 103 radially outward by the urging force of the spring. The external teeth 107 thereby mesh with the internal gear 106, so that the seat back is locked.
To tilt the locked seat back forward, it is unlocked and allowed to tilt with its angular position being remembered by the memory mechanism 110. In this case, a second operation lever provided separately from the first operation lever is operated to rotate the operation shaft 105 more largely than when unlocking and allowing the seat back to tilt without an angular position being remembered by the memory mechanism 110. Thereby, the cam 104 rotates largely with the operation shaft 105 clockwise in FIG. 26(B). The rotation of the cam 104 moves each of the locking members 103 radially inward. Each locking member 103 moves more than when the first operation lever is operated. As each locking member 103 moves, the engagement portion 112 disengages from the engagement receiving portion 114. When the seat back is tilted forward in this state, the memory plate 113 remains retained by the housing recess 111 by the friction between the memory plate 113 and the housing recess 111, as shown in FIG. 26(C). The engagement portion 112 slides on the inner circumferential surface 113B of the memory plate 113 counterclockwise. Since the memory plate 113 does not rotate relative to the housing recess 111 at this time, the engagement receiving portion 114 stays in position relative to the first member 101. In this way, the angular position of the seat back where it is located immediately before being tilted forward is remembered by the memory plate 113.
The seat back that has been tilted forward is then pulled back against the urging force of the forward tilt urging means. The engagement portion 112 then slides on the inner circumferential surface 113B of the memory plate 113 clockwise in FIG. 26(C), with the memory plate 113 retained by the housing recess 111. When the seat back comes to the angular position where it is located immediately before being tilted forward, the engagement portion 112 meets the engagement receiving portion 114, and each locking member 103 is pressed radially outward by the cam 104. The external teeth 107 thereby mesh with the internal gear 106, so that the seat back is locked. The angular position of the seat back where it is located immediately before being tilted forward can be remembered by such a simple structure, so that the seat back can be reset to the remembered angular position when it is pulled back up after being tilted forward.
However, in the seat reclining device described in Patent Document 1, when adjusting the locked seat back to a desired angular position, the engagement portion 112 is half engaged with the engagement receiving portion 114 as shown in FIG. 26(B). The locking members 103 rotate with the memory plate 113 relative to the housing recess 111 in this state. The memory plate 113 that has been reduced in diameter in the housing recess 111 is pressed against the inner circumferential surface 111A of the housing recess 111. Therefore, when the engagement portion 112 presses the engagement receiving portion 114 to enlarge the cut portion of the memory plate 113, the friction between the outer circumferential surface 113A of the memory plate 113 and the inner circumferential surface 111A of the housing recess 111 is increased. The sliding resistance of the memory plate 113 becomes accordingly large, which makes it harder to rotate the memory plate 113 relative to the housing recess 111. This consequently increases the operation load when adjusting the angular position of the seat back.
It is conceivable to reduce the surface pressure between the outer circumferential surface 113A of the memory plate 113 and the inner circumferential surface 111A of the housing recess 111 to reduce the sliding resistance of the memory plate 113. With this approach, however, if adopted, the memory plate 113 could no longer be retained by the housing recess 111 in an unlocked state where the seat back is allowed to tilt with an angular position of the seat back being remembered. The memory plate 113 would therefore rotate with the locking members 103 and could not fully exhibit its memory function.